Radio signal detector



Dec. l2, i950 D. H. ANDREWS 2,533,908

RADIO SIGNAL DETECTOR Filed Nov. 25, 1947 Patented Dec. 12, 1950 immo SIGNAL DETECTOR Donald H. Andrews, Baltimore, Md., assignor to Research Corporation, New York, N. Y., a corporation of New York Application November 25, 1947, Serial No. '7 87,959

3 Claims.

l This invention relates to a new radio signal detector and to radio signal receiver embodying The signal detector of the invention comprises essentially a conductive member, such as a Wire,

strip, film or coil, maintained at a temperature immediately below the superconductivity transition point of the member. Y

The electrical resistance and magnetic perme ability of a conductive substance decrease with decreasing temperature. At critical transition temperatures which differ for different subn stances, the electrical resistance and magnetic permeability suddenly fall substantially to zero. The transition from a condition of normal conductivity and permeability to superconductivity and extremely low permeability occurs, in gen eral, over a temperature range amounting to a small fraction of one degree. This range, the position and extent of which depends on the particular conductive material, may be termed the superconducting transition range, and. the temperature at which the rapid drop in electrical resistance begins to occur, that is, the upper end of the superconductive transition range, will be termed the superconductivity transition temperature.

I have found that conductive substances, maintained at a temperature immediately below the superconductivity transition temperature of the substance, both Within and below the superconductivity transition range, act as effective detectors of radio frequency signals. While a number of metals and metallic compounds are suitable for providing the conductive members, such as tin, lead, aluminum, columbium (niobium), and columbium (niobium) carbide with transition temperatures of about 3.7 K., 7 K., l K., 9 K. and 10 K., respectively, columbium (niobium) nitride (CbN) is particularly useful because its transition temperature is somewhat above the triple point of hydrogen at 14 K., so that liquid hydrogen under vacuum may be used as a refrigerating medium.

A radio receiver embodying the principles of the invention may comprise a tuned circuit including a conductive member, for example, columbium nitride, maintained at a temperature immediately below its Superconductivity transition temperature, an audio frequency amplifying circuit coupled to the tuned circuit, and a loudspeaker, cathode ray oscilloscope, or other audio frequency responsive device connected to the output of the amplifying circuit. Such a receiver will effectively receive modulated radio frequency signals over the frequency range of at least 0.1 to 2l) megacycles. The receiver of the invention is characterized by a very favorable signal-to-noise ratio in the reception of audio 4frequency modulated radio -irequency signals.

The invention will be more particularly described ior the purpose of illustration with reference to the accompanying drawings, in which:

Fig. 1 is a graph illustrating the relation of the resistance of columbium nitride to its tem.- perature in the neighborhood of its superconducting transition range;

Fig. 2 is a diagrammatic representation in scctional elevation of a cryostat suitable for use in the invention;

Fig. 3 is a fragmentary detail showing the superconducting member of the deviceofv Fig. 2 in plan view, and

Fig. 4 is a circuit diagram of a radio receiver embodying the principles of the invention.

Fig. 1 shows the relation of the resistance of a typical sample of columbium nitride at temperatures shortly above the triple point of hydrogen. It will be seen that in the sample illustrated the resistance begins to drop very rapidly at a temperature just below 14.5 K. indicated by point A, representing the superconductivity transition temperature as defined herein, and has fallen to a very lcw level within a small part of a degree at point B. The range between points A and B represents the superconductivity transition range, within which the particular Lsample of columbium nitride illustrated may be effectively used as a radio signal detecting element in accordance with the invention.

The cryostat diagrammatically illustrated in Figs. 2 and 3 comprises a plurality of concentric annular cylindrical copper containers concentrically arranged about a central copper post iii. The innermost container Il is normally sup plied with liquid hydrogen, and the intermediate container I2 with liquid nitrogen. The outer container i3 provides a vacuum jacket for the cryostat. The containers ll and IZ are mounted at their tops on an insulating spacer I4 which also carries the cover I5 and radiation shield it. The latter members may advantageously carry a centrally located plastic observation window il. The post l@ is supported from the bottom by insulating ring IS. The containers are provided with suitable inlets 2l, 22 and vents 23,

and a connection 25 for evacuating the cryostat.

Mounted on the top or post I0 is a strip 2l! of columbium nitride Provided at each end With in container I I and a supply of liquid nitrogen.

in container l2, and the cryostat is evacuated, the hydrogen is maintained at the triple point 14 K. The upper end of post I0 is then readily maintained in the transition range of the colum-V bium nitride by a suitable current in coil I9.

In the circuit diagram of Fig. 4, the superconductive strip 2!! is shown in a tuned circuit including variable capacity 3l] and the primary of audio frequency transformer 3l. An adjustable source of current 32 may be included in the circuit, as a small current through the strip 20 may improve its sensitivity as a detector and the current' may be used in' adjusting the temperature of the strip'.

The secondary of transformer 3| forms part o1" an audio frequency circuit includingy audio frequency amplifier 33 the output of which is supplied to loudspeaker 34.

It will, of course, beiobvious to those skilled in the art of radio communication that the circuit shown in Fig. 4 is subject to a wide variety of modication of circuit elements and their a1'- rangement Without departing from the principles 0f the invention as described herein and as dened in the claims hereof.

I claim:

1. In a radio signal receiver, a tuned circuit including a columbium nitride member maintained at a temperature below its superconductivity transition temperature.

2. A radioreceiver comprising in combination a tuned circuit including a conductive member, means for maintaining said member at a temperature below its superconductivity transition temperature, an audio frequency amplifying circuit coupled to said tuned circuit, and an audio frequency responsive device connected to the output of said audio frequency amplifying circuit.

3. A radio receiver comprising in combination a tuned circuit including a columbium nitride member, means for maintaining said member at a temperature below its superconductivity transition temperature, an audio frequency amplifying circuit coupled to said tuned circuit, and an audio frequency responsive device connected to the output of said audio frequency amplifying circuit.

DONALD H. ANDREWS.

REFERENCES CITED The following references are of record inthe le of' this. patent:

UNITED STATES PATENTS Number Name Date 2,128,750 Kriebel Aug. 30, 1938 2,189,122 Andrews Feb. 6, 1940 OTHER REFERENCES Burton, Supercon'ductivity, Univ. of Toronto Press, 1934, Scientific Library.

National Bureau of Standards, Journal ofRe search, volume 20, Research Paper 1070, published February 1938', volume 20. 

